The insider's guide to nuclear fusion

By Sunaina Gulati for CNN

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LONDON, England (CNN) -- The European Union, along with six other nations have signed a €10 billion (US$12.8 billion) pact to build the world's most advanced nuclear fusion reactor aimed at developing a cheaper, cleaner and safer energy source to replace fossil fuels. We tell you what you need to know about the deal.

What is this all about?

As you already know, fossil fuels are a backbone of industrialized nations. Oil, coal, natural gas or similar carbon-based sources of energy fall into this category and they are currently the primary source of relatively-cheap energy. But, they also are a major source of environmental pollution. Combustion of these fuels is considered to be the largest contributing factor to the release of greenhouse gases, which many scientists believe are largely responsible for global warming and climate change. Thus, this pact is a huge step towards combating climate change.

What is the new agreement?

After years of negotiations, 30 nations including China, the 24 European Union countries, India, Japan, South Korea, Russia and the United States this week signed an agreement to build the world's most advanced nuclear fusion reactor -- the International Thermonuclear Experimental Reactor (ITER) -- at a site in France.

How will it work?

ITER is an experimental reactor that once complete will attempt to ape the process by which stars, including the sun, produce energy. It will use the same nuclear fusion reaction to produce an inexhaustible supply of energy possibly replacing oil and gas. Deuterium, the major fuel that will be used to operate this reactor will be extracted from seawater.

Sounds explosive! Tell me more.

Nuclear fusion involves the bringing together of atomic nuclei. An atom's nucleus consists of protons (positive charge) and neutrons (no charge.) The reaction, which takes place at extremely high temperatures, joins two light atomic nuclei to form heavier ones and in this process releases large amounts of energy. Scientists say nuclear fusion could provide a sustainable answer to concerns of pollution caused by fossil fuels.

But, is it safe?

It is claimed to be. And it does have some key features that make it such an attractive option for future energy supply. Fusion plants don't generate greenhouse gases such as carbon dioxide -- blamed by many scientists for causing global warming -- or other gases that have harmful effects on the environment. Experts also say that the process in itself is inherently safe because equipment failure will simply result in a system shutdown. They also say no chain reaction is involved and the reaction is thermally self-limiting. Due to its experimental nature, it is possible for the plant to sometimes operate at higher power levels than planned, but it is said that this can be easily brought under control in a matter of seconds.

Don't nuclear plants produce a lot of waste that is also potentially damaging?

Yes. But the waste amount is considered minimal and will be safe to handle in a relatively modest timescale of 50 to a 100 years. Fusion scientists also say that its waste will be less dangerous as compared to a large coal-fired power plant that would have run for the same period of time.

Sounds too good to be true.

Maybe it is. Critics say that it will be at least 40 to 50 years before a viable reactor is built, if one is built at all. It might be 2050 before it all comes together and even then, there is no guarantee. Moreover, construction of the 500-megawatt reactor is forecast to cost about five billion euros ($6.41 billion.) An additional five billion euros would be needed to operate it over a 20-year period.

Then why so much excitement?

While other forms of energy production continue to be explored, not many can rival the amount of energy a fusion process can generate. Some green campaigners are still unhappy though, as they say fusion is neither clean nor safe.

Where will the reactor be built?

The southern France town of Cadarache, just north of Marseille, has been selected as the site to build the reactor beating stiff competition from places like the northern Japanese village of Rokkasho.

What else should we know?

It is expected to create about 10,000 jobs. French President Jacques Chirac says: "If nothing changes, humanity will have consumed, in 200 years, most of the fossil fuel resources accumulated over hundreds of millions of years." He adds: "It (the ITER project) is the victory of the general interest of humanity."